Fractal dynamics of human gait: a reassessment of the 1996 data of Hausdorff et al

EA 2991 Motor Efficiency and Deficiency, University Montpellier I, Montpellier, France Submitted 12 June 2008 ; accepted in final form 18 February 2009 We propose in this paper a reassessment of the original data of Hausdorff et al. (Hausdorff JM, Purdon PL, Peng C-K, Ladin Z, Wei JY, Goldberger AR. J Appl Physiol 80: 1448–1457, 1996). We confirm, using autoregressive fractionally integrated moving average modeling, the presence of genuine fractal correlations in stride interval series in self-paced conditions. In contrast with the conclusions of the authors, we show that correlations did not disappear in metronomic conditions. The series of stride intervals presented antipersistent correlations, and 1/ f fluctuations were evidenced in the asynchronies to the metronome. We show that the super central pattern generator model (West B, Scafetta N. Phys Rev E Stat Nonlin Soft Matter Phys 67: 051917, 2003) allows accounting for the experimentally observed correlations in both self-paced and metronomic conditions, by the simple setting of the coupling strength parameter. We conclude that 1/ f fluctuations in gait are not overridden by supraspinal influences when walking is paced by a metronome. The source of 1/ f noise is still at work in this condition, but expressed differently under the influence of a continuous coupling process. gait dynamics; 1/ f fluctuations; metronomic driving; modeling Address for reprint requests and other correspondence: D. Delignières, Faculty of Sport Sciences, Univ. Montpellier I, 700 Ave. du Pic Saint Loup, 34090 Montpellier, France (e-mail: didier.delignieres{at}univ-montp1.fr )